1. Field of the Invention
The present invention relates to a display system in which a device including a conductive thin plate such as a touch panel is provided on a display device such as a liquid crystal display device so that the display device and the conductive thin plate are integrated with each other.
2. Description of the Related Art
An input device such as a touch panel which detects a point on a panel surface which point is touched with a pen or a finger includes a conductive sheet. Patent Document 1 (Japanese Unexamined Patent Publication No. 167677/2003 (Tokukai 2003-167677) discloses a touch-panel-integrated display device in which the input device and the display device such as a liquid crystal display device are combined with each other. The touch panel is electrically connected to a touch panel controller so as to detect a position via which information is inputted to the touch panel with a pen. Normally, the touch-panel-integrated display device is arranged so that the touch panel controller is completely independent from a driving circuit for driving the display device.
Recently, the above-mentioned touch-panel-integrated display device (display system) has been more widely used as a portable device, so that the display device has become thinner and lighter. Thus, there are tendencies to make the device thinner by making the glass constituting the touch panel thinner and to make the device lighter by using plastic instead of glass.
In a case of using such a touch panel, this raises the following problem: a driving signal of the display device influences the touch panel, so that the touch panel is vibrated, which results in noise. This noise is generated as follows. The display device or the touch panel is electrically charged by static electricity generated in the production step, sliding of the pen when in contact with the touch panel, friction generated in pressing the pen against the panel surface, exfoliation, and the like, and an electric charge thereof is influenced by the driving signal of the display device, so that a force which varies with the passage of time is generated. In a portable information terminal having a sound collecting function or a telephone function, the noise is audible, so that the foregoing problem is more noticeable.
There is presently known a technique for suppressing the occurrence of abnormal minute vibration or abnormal noise in a thinner liquid crystal display device (see Patent Document 2 (Japanese Unexamined Patent Publication No. 295162/2003 (Tokukai 2003-295162). However, it has not been reported or disclosed that any discovery or study has been made regarding the above-described problems with the display device provided with the device having the conductive sheet such as the touch panel. Thus, the inventors of the present application have not found any document which identifies or recognizes the above-described problems.